Low cost high ductility cast aluminum alloy

ABSTRACT

An aluminum alloy for casting into a component, such as an automotive vehicle component, is provided. The aluminum alloy includes a reduced amount of silicon (Si), specifically 0.1 weight percent (wt. %) to less than 7.0 wt. %, and preferably 4.0 wt. % or less, to achieve improved ductility and elongation. The aluminum alloy can also include additional alloying elements to achieve desired properties. For example, antimony, calcium, and/or bismuth can be included to counter any detrimental effect of the low silicon content on hot cracking behavior. Zinc can be added to increase strength; and cerium can be added to further increase ductility. The aluminum alloy is typically formed by modifying recycled wrought aluminum, such as a 5000 series or 6000 series aluminum alloy, or by modifying a recycled cast 300 series aluminum alloy.

CROSS REFERENCE TO RELATED APPLICATION

This U.S. Patent Application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/134,072, filed on Mar. 17, 2015, and entitled “Low Cost High Ductility Cast Aluminum Alloy,” the entire disclosure of the application being considered part of the disclosure of this application and hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to an aluminum alloy for casting, a method of forming the aluminum alloy, an automotive vehicle component formed of the cast aluminum alloy, and a method of manufacturing the cast component.

2. Related Art

Casting of aluminum alloys is oftentimes used in the automotive industry to form lightweight components, including complex structural, body-in-white, suspension, and chassis components. There are many types of known casting processes, for example high pressure die casting, low pressure casting, and squeeze casting. The die is typically formed of a hardened tool steel. Although the casting equipment is expensive, the cost per component formed is relatively low, which makes the process suitable for high volume production.

However, improvements to the casting process and materials used in the casting process are desired. For example, an aluminum alloy capable of forming a component having higher ductility, without loss of fluidity or castability, is desired. The aluminum alloy should also be resistant to damage associated with hot cracking, soldering, shrinkage, and corrosion. In addition, although lightweight components are desired, the components should still provide a high strength and toughness.

SUMMARY OF THE INVENTION

One aspect of the invention provides an improved aluminum alloy for casting. The aluminum alloy includes aluminum in an amount of at least 70 weight percent (wt. %) and silicon in an amount of 0.1 wt. % to less than 7.0 wt. %, based on the total weight of the aluminum alloy. This amount of silicon is reduced amount compared to other aluminum alloys used for casting which typically include 7.0 wt. % to 11.0 wt. % silicon. The reduced amount of silicon provides a smaller eutectic phase and thus improved elongation, without loss of castability. The reduced amount of silicon also reduces the cost of the aluminum alloy. Additional alloying elements can also be present in the aluminum alloy to improve resistance to hot cracking, soldering, shrinkage, and corrosion, and also to achieve a desired strength and toughness, or even higher ductility.

A method for manufacturing an improved aluminum alloy for casting is also provided. The method includes providing an aluminum alloy, wherein the aluminum alloy is selected from a 300 series aluminum alloy, 5000 series aluminum alloy, and 6000 series aluminum alloy. The method further includes melting the aluminum alloy; and adding silicon to the melted aluminum alloy so that the total amount of silicon present ranges from 0.1 wt. % to less than 7.0 wt. %, based on the total weight of the melted aluminum alloy.

Another aspect of the invention provides a cast component formed of the improved aluminum alloy. The cast component has increased ductility and elongation, compared to the same component formed of the comparative aluminum alloys with greater amounts of silicon.

A method for manufacturing the component by casting the improved aluminum alloy is also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a graph illustrating the effect of silicon content on fluidity of an aluminum-silicon binary alloy;

FIG. 2 illustrates a portion of an example component formed of an aluminum alloy according to an embodiment of the invention;

FIG. 3 is a photomicrograph of the component of FIG. 2; and

FIG. 4 illustrates method steps used to form the component of FIG. 2 according to an example embodiment.

DESCRIPTION OF THE ENABLING EMBODIMENT

One aspect of the invention provides an improved aluminum alloy for casting components, such as a lightweight automotive vehicle component, is provided. Examples of such components include structural, body-in-white, suspension, or chassis components. The aluminum alloy provides a component with improved ductility and elongation, and without loss of fluidity or castability. The aluminum alloy is also less expensive than other aluminum alloys used for casting, which is especially beneficial for high volume production.

The improved aluminum alloy is aluminum-based, and thus typically includes aluminum in an amount of at least 70 weight percent (wt. %), based on the total weight of the aluminum alloy. In one embodiment, the aluminum alloy is formed by modifying a 5000 series alloy, which includes 88.2 wt. % to 99.8 wt. % aluminum. In another embodiment, the aluminum alloy is formed by modifying a 6000 series alloy, which includes 91.7 wt. % to 99.6 wt. % aluminum. However, other amounts of aluminum could be used.

The aluminum alloy also includes an amount of silicon (Si) which helps achieve the improved elongation and ductility with reduced costs. The amount of silicon ranges from 0.1 to less than 7.0 wt. %, and typically 2.0 to 4.0 wt. %, based on the total weight of the aluminum alloy. This amount of silicon is reduced compared to other aluminum alloys used for casting, which typically include 7.0 wt. % to 11.0 wt. % silicon. The lower amount of silicon present in the improved aluminum alloy creates a smaller eutectic phase, which leads to increased elongation in the finished component, as the eutectic phase is one of the main limitations for elongation. The elongation of a component formed of the improved aluminum alloy with reduced silicon content is typically 8% to 10%.

The reduced amount of silicon also reduces the total cost of the aluminum alloy. The castability, strength, and toughness of the aluminum alloy can also be adjusted based on the amount of silicon. In addition, it has been found that the reduced amount of silicon does not sacrifice fluidity or castability of the aluminum alloy, when compared to the other aluminum alloys which include 7.0 wt. % silicon or greater. In some cases, the castability of the improved aluminum alloy is better than that of the other aluminum alloys including 7.0 wt. % silicon or greater. FIG. 1 is a graph illustrating the effect of silicon content on fluidity of an aluminum-silicon binary alloy.

Additional alloying elements can also be present in the improved aluminum alloy to further improve elongation and ductility, or to achieve the desired strength and toughness. For example, magnesium (Mg), manganese (Mn), cerium (Ce), and/or iron (Fe) can be added to further improve ductility, castability, strength, ductility, and/or toughness. The aluminum alloy can also include at least one of copper (Cu) and zinc (Zn) to increase strength, preferably without negatively impacting corrosion resistance. The additional alloying elements can provide other metallurgical effects as well, such as improved resistance to hot cracking, soldering, shrinkage, and corrosion. Special properties or other metallurgical effects can be achieved by adding at least one of titanium (Ti), strontium (Sr), calcium (Ca), zirconium (Zr), bismuth (Bi), antimony (Sb), boron (B), molybdenum (Mo), scandium (Sc), and rhenium (Re). In an exemplary embodiment, antimony, calcium, and/or bismuth is added to counter any detrimental effect of the low silicon content on hot cracking behavior; zinc is added to increase strength, and cerium is added to further increase ductility. FIG. 2 illustrates a portion of an example component 10 formed of the improved aluminum alloy, and FIG. 3 is a photomicrograph 12 of a portion of the component 10 shown in FIG. 2.

Another aspect of the invention provides a method of manufacturing the aluminum alloy. FIG. 4 illustrates steps of the method according to an example embodiment. The aluminum alloy is preferable formed from recycled wrought aluminum, such as a 5000 series or 6000 series aluminum alloy. Recycled cast aluminum alloys in the 300 series, such as Al—Si—Mg alloys, could alternatively be used as the base material. Other aluminum-based materials that could be used to form the improved aluminum alloy are sold by Cosma International or Magna International, such as Aural-4 or a Promatek self-hardened Al—Si—Mg—Zn alloy. Manufacturing the improved aluminum alloy from one of the recycled materials lowers the raw material cost, as it takes 95% less energy to recycle an aluminum alloy than to create it from primary elements.

The method typically begins by melting the recycled wrought aluminum, or other base aluminum alloy. The melting step can be conducted by an induction melter, or another source of heat. Once the base aluminum alloy is melted, the method includes adding silicon to the melt and mixing the silicon with the base aluminum alloy so that the total amount of silicon ranges from 0.1 wt. % to less than 7.0 wt. %, and preferably 4.0 wt. % or less, based on the total weight of the melted aluminum alloy, i.e. the final alloy composition. The additional alloying elements, discussed above, can be added to the melted mixture to form the improved aluminum alloy. Alternatively, the additional alloying elements could be present in the wrought aluminum or other base aluminum alloy. Once all of the elements are mixed together, the aluminum alloy is ready for casting.

Another aspect of the invention provides a cast component for an automotive vehicle formed of the improved aluminum alloy, and a method for manufacturing the cast component. Any casting process used to form components from an aluminum-based material can be used with the improved aluminum alloy, for example high pressure die casting, low pressure casting, or squeeze casting. In one example embodiment, the casting process is a die casting process, which typically includes forcing the molten aluminum alloy into an unheated die or mold cavity under pressure. The die is typically formed from hardened tool steel. As discussed above, the castability and fluidity of the molten aluminum alloy with the reduced amount of silicon is equal to or slightly better than other aluminum alloys with higher amounts of silicon. The molten aluminum is formed to a solid component having the shape of the mold, which can be a complex shape. Many different types of components can be formed by the casting process, for example, a structural, body-in-white, suspension, or chassis component. After the casting process, the method can include an optional heat treating process or other finishing processes. However, it has been found that a heat treatment process may not be necessary when the component is formed from the improved aluminum alloy, which would provide the advantage of reduced process time and costs.

The component formed from the improved aluminum alloy has improved ductility and elongation due to the lower amount of silicon in the aluminum alloy. In addition, the aluminum alloy can include additional alloying elements to improve resistance to hot cracking, soldering, shrinkage, and corrosion, and also to achieve a desired strength and toughness, or even higher ductility.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the following claims. 

What is claimed is:
 1. An aluminum alloy for casting into a component, comprising: aluminum in an amount of at least 70 weight percent (wt. %) and silicon in an amount of 0.1 wt. % to less than 7.0 wt. %, based on the total weight of the aluminum alloy.
 2. The aluminum alloy of claim 1, wherein the silicon is present in an amount of 2.0 wt. % to 4.0 wt. %, based on the total weight of the aluminum alloy.
 3. The aluminum alloy of claim 1 further including at least one of magnesium (Mg), manganese (Mn), cerium (Ce), iron (Fe), copper (Cu), zinc (Zn), titanium (Ti), strontium (Sr), calcium (Ca), zirconium (Zr), bismuth (Bi), antimony (Sb), boron (B), molybdenum (Mo), scandium (Sc), and rhenium (Re).
 4. The aluminum alloy of claim 3 including zinc (Zn); cerium (Ce); and at least one of calcium (Ca), antimony (Sb), and bismuth (Bi).
 5. A cast component, comprising: an aluminum alloy including aluminum in an amount of at least 70 wt. % and silicon in an amount of 0.1 wt. % to less than 7.0 wt. %, based on the total weight of the aluminum alloy.
 6. The cast component of claim 5, wherein the silicon is present in an amount of 2.0 wt. % to 4.0 wt. %, based on the total weight of the aluminum alloy.
 7. The cast component of claim 5, wherein the aluminum alloy further includes at least one of magnesium (Mg), manganese (Mn), cerium (Ce), iron (Fe), copper (Cu), zinc (Zn), titanium (Ti), strontium (Sr), calcium (Ca), zirconium (Zr), bismuth (Bi), antimony (Sb), boron (B), molybdenum (Mo), scandium (Sc), and rhenium (Re).
 8. The cast component of claim 7 including zinc (Zn); cerium (Ce); and at least one of calcium (Ca), antimony (Sb), and bismuth (Bi).
 9. The cast component of claim 5, wherein the component has an elongation ranging from 8% to 10%.
 10. The cast component of claim 5, wherein the component is a structural, body-in-white, suspension, or chassis component for an automotive vehicle.
 11. A method of manufacturing an aluminum alloy for casting into a component, comprising the steps of: providing an aluminum alloy, wherein the aluminum alloy is selected from a 300 series aluminum alloy, 5000 series aluminum alloy, and 6000 series aluminum alloy; melting the aluminum alloy; and adding silicon to the melted aluminum alloy so that the total amount of silicon present ranges from 0.1 wt. % to less than 7.0 wt. %, based on the total weight of the melted aluminum alloy.
 12. The method of claim 11, wherein the step of adding silicon includes adding the silicon in an amount so that the total amount of silicon present ranges from 2.0 wt. % to 4.0 wt. %, based on the total weight of the melted aluminum alloy.
 13. The method of claim 11, wherein the aluminum alloy includes at least one of magnesium (Mg), manganese (Mn), cerium (Ce), iron (Fe), copper (Cu), zinc (Zn), titanium (Ti), strontium (Sr), calcium (Ca), zirconium (Zr), bismuth (Bi), antimony (Sb), boron (B), molybdenum (Mo), scandium (Sc), and rhenium (Re) after the melting step.
 14. The method of claim 11, wherein the aluminum alloy provided includes zinc (Zn); cerium (Ce); and at least one of calcium (Ca), antimony (Sb), and bismuth (Bi) after the melting step.
 15. The method of claim 11, wherein the step of providing the aluminum alloy includes recycling a 300 series aluminum alloy, 5000 series aluminum alloy, or 6000 series aluminum alloy.
 16. A method of manufacturing a cast component, comprising the steps of: providing an aluminum alloy, wherein the aluminum alloy is selected from a 300 series aluminum alloy, 5000 series aluminum alloy, and 6000 series aluminum alloy; melting the aluminum alloy; adding silicon to the melted aluminum alloy so that the total amount of silicon present ranges from 0.1 wt. % to less than 7.0 wt. %, based on the total weight of the melted aluminum alloy; and casting the melted aluminum alloy.
 17. The method of claim 16, wherein the casting step includes high pressure die casting, low pressure casting, or squeeze casting.
 18. The method of claim 16, wherein the step of adding the silicon includes adding the silicon to the melted aluminum alloy so that the total amount of silicon present ranges from 2.0 wt. % to 4.0 wt. %, based on the total weight of the melted aluminum alloy.
 19. The method of claim 16, wherein the casting step includes forming a component having an elongation ranging from 8% to 10%.
 20. The method of claim 16, wherein the casting step includes forming the melted aluminum alloy into a structural, body-in-white, suspension, or chassis component for an automotive vehicle. 